What Do You See?
A boy pretending he is on a rollarcoaster by having someone push him blindfolded on a rolling chair What Do You Think? Which part of the roller-coaster ride produces the loudest screams? Why?
The speed and the loops produce the loudest screams because it is exciting and scary
Homework 3-28-11 El Toro
The track is made so that it snaps together like Lego pieces and is made of more layers of wood that are tightly bonded together instead of nailed together by hand like a traditional wooden roller coaster.
Constant speed
Goliath
540-degree spiral
Over water
Checking Up 1. Explain the difference between distance and displacement. Displacement has magnitude and direction and distance has direction. 2. You went to school and back home, a total distance of 2km. What is your displacement? 3.What is the difference between speed and velocity? Velocity has a direction and speed doesn’t 4. How can you find the acceleration of an object? By using its change in velocity and its time. Then you do v/t to find the acceleration. Physics to Go
1.
Ch4_S1_PTG1.png
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2. Identify where the biggest trill will be in Th Terminator Express roller coaste. Explain why this will be the big thrill
The drops and the horizontal loop because they have the change in acceleration and direction that makes the ride exciting 3. Speed by itself does not produce thrills. Living on Earth, you already have a big speed, since Earth is constantly turning a) Earth makes a complete revolution once every 24h. La Paz, Bolivia is close to the Equator and travels a large circumference in 24h. Oslo, Norway is close to the Arctic Circle and travels a smaller circumference in 24 h. Which city has the greater speed? Bolivia b) The circumference of Earth’s Equator is about 40,000 km. It requires one day or 24 h to complete one revolution. Calculate the speed you are traveling on Earth if you are at the Equator
Ch4_S1_PTG3b.png
c) Why do you not get a big thrill going at such a high speed? Because there is no acceleration happening 4. A roller-coaster rider traveling in a straight line changes from a speed of 4 m/s to 16 m/s in 3 s. Calculate the acceleration of the ride.
Ch4_S1_PTG4.png
5. Identify the following situations as an example of either distance, displacement, speed, velocity, or acceleration. a) a car traveling at 50km/h Speed b) a student riding a bike at 4m/s toward home Velocity c) a roller-coaster ride whips around a left turn at 5m/s Acceleration d) a roller-coaster car is dragged up a hills 12 m tall traveling at 3m/s. Displacement and Velocity e) a train ride takes you 150 km northeast Displacement 6. A lab cart is 10 cm long. It travels through a velocimeter in 2 s. Calculate the cart’s speed.
Ch4_S1_PTG6.png
7. A second lab cart is 5 cm long. If it were traveling at the same speed as the casrt in Question 6, what would the velocimeter record as the elapsed time?
Ch4_S1_PTG7.png
8. Your vehicle accelerates from 0 to 25 m/s (about 55mi/h) in 10 s while traveling down a straight street. What is the acceleration of your vehicle?
Ch4_S1_PTG8.png
What do you think now? I think that drops, loops, and change in acceleration will have provide the excitement because they are the unexpected
Section 2
What Do You See? People are having fun on the downhill and the staright slow parts they are bored
What Do You Think? The 90 angle one because it is a larger angle
Physics Talk The initial height of the ball is determined by the height of where the ball starts. KE and GPE depend on the mass of the ball. As the ball comes down the incline the GPE decreases and the KE increases
Checking Up 1. What effect does changing the length of the incline have on the speed of a ball when it rolls to the bottom? It had no effect on the speed of the ball 2. How does the gravitational potential energy of an object change with its height? With its mass? As the height goes up the GPE goes up. The mass goes up the GPE goes up also. 3. How does the kinetic energy of an object change with its speed? With its mass? As the speed goes the up KE goes up. The mass goes up as the KE goes up also. 4. As a roller-coaster car rolls down a hill, what happens to the gravitational potential energy it loses? Its put into KE 5. If a roller-coaster car has 40,000 J of GPE when at rest on the top of a hills how much KE does it have when it ¾ of the way down the hills 30,000
Physics To Go 1. For which track is the speed of the car greatest at the bottom? They are the same 3. Mass of car = 200kg g = 10m/s^2
Position of car = height (m)
GPE (J) = mgh
KE( J) = ½ mv^2
GPE + KE (J)
Top (30)
60,000
309
60,000
Bottom (0)
312
60,000
60,000
Halfway down (15)
30,000
30,000
60,000
Three-quarters way down (7.5)
15,000
45,000
60,000
PTG3_Ch4_Sec2.png
Mass of car = 300kg and g = 10m/s^2
Position of car = height (m)
GPE (J) = mgh
KE( J) = ½ mv^2
GPE + KE (J)
Top (25)
75,000
332
75,000
Bottom (0)
335
75,000
75,000
Halfway down (12.5)
37,500
37,500
75,000
Three-quarters way down (5)
15,000
60,000
75,000
PTG5_Ch4_Sec2.png
7. A pendulum is lifted to a height of .75 m. The mass of the bob is .2 kg. a) Calculate the GPE at the top.
Picture_2.png
b) Find the KE of the bob at the bottom
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c) At what position of the bob will the GPE and KE be equal The middle 8. In the early morning, a roller-coaster train (set of cars hookes together) only has 6 passengers. In the afternoon it has 26 passenger. Will the sppeed of the roller coaster change with more passengers aboard? Explain your answer It would not change because GPE and Ke both have mass so they cancel eacho ther out making irrelevant 9. To the right is a side view of a roller coaster that starts from rest at position A. a)At which point is the roller-coaster car traveling the fastest? Explain. From A-B because it is accelerating the most b) At which two points is the roller-coaster car traveling at the speed? Explain. B and G because they are both changing direction c) Is the roller coaster car traveling faster at E or D? Explain. D because it has finished accelerating
10. Above and to the right is a side view of a roller coaster that starts from rest at position A b) Why can’t the roller coaster each point H Because it does not have enough KE to get itself up the hill
Position of car
Height (m)
GPE (J) = mgh
KE (J) = 1/2mv^2
GPE + KE (J)
Bottom of hill
10000
60000
Top of hill
50000
10000
60000
Top of loop
30000
10000
60000
Horizontal loop
10000
60000
What Do You Think Now?
They will be the same speed because they are both starting at the same height. Roller coaster B will provide the most thrills because it is steep.
Section 3
What Do You See?
Students measuring how far a frog bouncy toy goes with a meter stick and a photogate timer
What Do You Think? How does the roller coaster today get up to its highest point?
They are now motorized Does it cost more to lift the roller coaster if it full of people?
No Physics talk
Spring potential energy (EPE) is the energy stored in a spring due to its compression or stretch. The equation is EPE= 1/2kx2. Checking up 1. What happens to the spring potential energy of a “pop-ip” toy after it leaps off the table EPE would turn into KE upon flight 2. A ”pop-up” toy had 2J of spring potential energy before popping. How much kinetic energy will the toy have just after leaving the table 2J 3. A “pop-up” toy has 2J of spring potential energy before popping. How much gravitational potential energy will it have at the top? 2J 4. What two factors determine the amount of spring potential energy that is stored in a psring The distance it is compressed and its constant (k) Physics To Go 5. Why can the second hill of the roller coaster not be higher than the girst hill? The amount of KE needed to get over the second hill cannot be larger then the amount needed for the first. 6. Why does the roller coaster not continue forever and go back and forth and up and down the hills over and over again? There is work and friction that slows the roller coaster 7. A roller coaster of mass 300 kg ascends to a hright of 15m. How much electrical energy was required to raise the cars to this height?
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8.A roller-coaster car has a mass of 400kg and a speed of 15m/s a)What is the KE of the roller-coaster car?
PTG_Ch4_Sec3_8a.png
b)What will be the GPE of this roller-coaster car at its highest point, where KE=0 at that point 45,000J c)How high can the roller-coaster car go with this much energy?
PTG_Ch4_Sec_3_8c.png
9. A bal is thrown upward from Earth’s surface. While the ball is rising, is its gravitational potential energy increasing, decreasing, or remaining the same? It is increasing, as h increases GPE increases 10. Three people of equal mass climb a mountain using paths A, B, and C shown in the diagram. Along which path(s) does a person gain the greatest amount of GPE from start to finish.: A only, B only, C only, or is the gain the same along all paths They all reach the same end point and reach the same GPE 11. In an experiment similar to your toy, the mass of the spring toy was 0.020 kg. The height that the toy rose to was 0.40 m. The initial speed of the spring toy as measured by the velocimeter was 2.7m/s. a)Do the GPE and the KE both give approximately the same values?
PTG_Ch4_Sec3_11a.png
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Yes. b) What is the EPE before the toy pops 0.13 m 12. A roller coaster begins at a height of 18 m. The mass of the roller coaster and passengers is 300 kg. When the roller coaster reaches the bottom, its brakes fail. An emergency spring must bring the coaster to rest a) What must be the spring constant of this spring if it will be compressed by 4m? 6600 N/m b) How much will the spring compress if an additional 100 kg of people are aboard? 4.62m 13. An umbrella has an automatic opening mechanism. When the umbrella is closed, a spring is compressed. The spring constant is 40 N/m and the spring is compressed 0.3m. What is the KE of the umbrella when it begins to open?
PTG_C4_Sec3_13.png
Section 4
What do you see? The more gravity a roller coaster has the faster you go. What do you think? Gravity has a direction to the Earth's crust. Australia can be held on Earth because they are being pushed towards the core. Physics Talk Earth's gravitational Field is the gravitational influence in the space around a massive object. It needs a source of the field and a second object to interact with the field, the response object. Gravitational field lines show the direction of the gravitational field, that the field is stronger where the lines are close together and weaker where the lines are further apart, some points of the field and that the field extends to infinity. Inverse-Square Relationship is the relationship between the magnitude of a gravitational foe and the distance from the mass. It also describes how electrostatic forces depend on the distance from an electrical charge. Newton's law of universal gravitation is that all bodies with mass attract all other bodies with mass. The force is proportional to the product of the two masses and gets stronger as either mass gets larger. Gravity is the force of attraction between two bodies due to their masses. The Universal Gravitation equation is
Ch4_Sec4_PT.png
Fg is the force between bodies, r is the distance between their centers m1 and m2 are the masses of the bodies, G is the universal constant that is 6.67x10-11 N*m^2/kg^2 Checking up 1. What is the direction of the gravitational field in your classroom? The direction of the strongest gravitational field is to the center of the earth. 2. Using the idea of field lines, where is the gravitational field the strongest? The closer you are to an object, the stronger the field. 3. If you triple the distance between two masses, what happens to the force gravity between the two masses? You divide it by 9 4. What is the force that holds the Moon in its orbit around Earth? Gravity 5. Approximately white is the shape of the orbit of the planets around the Sun? Circular Physics To Go 1. The gravitational force beween two asteroids is 500 N. What would the force be if the distance between them doubled? 250N 3. Why does everyone trust in gravity We have always believed in it and there is no reason not to 4. Compare the acceleration due to gravity at the top and bottom of a roller-coaster ride. They are equal 5. a) Which is closer to the Moon- the middle of Earth or the water on the side of Earth facing the Moon ? The water on the side of the earth facing the moon b) Suggest an explanation for high tides on the side of Earth facing the Moon. Only the water is effected by the gravity of the moon because it is weaker then the Earth’s. c) Use your answer to a) to propose an explanation for the uneven distribution of water on Earth’s surface, as shown in the diagram The force of gravity is stronger when the moon and the water get closer 6. Astronauts on many Shuttle fligts study the effects of “free fall.” Fish taken aboard the Shuttle react to “free fall” by swimming in circles. “Free fall” minics what you feel if gravity were not present a) How would a fish’s life be different without gravity They would die because there wouldn't be a body of water for them to live in b) Does gravity hold a fish “down” on Earth? Yes 7. Two objects have a tiny, but measurable gravitational force of attraction between them. How will that force change if the distance between the objects is a) divided by 4 b) divided by 9 c) divided by 16 d) multiplied by 4 8. Two objects have a tiny, but measurable gravitational force of attraction between them. How will that force change if the mass of one of the objects is a) divided by 4 b) divided by 9 c) divided by 16 d) multiplied by 4 9. Two objects have a tin, but measurable gravitational force of attraction between them. How will that force change if the mass of both of the objects is a) doubled b) tripled c) quadrupled d) halved 10. Two objects have a tin, but measurable gravitational force of attraction between them. How will that force change if the following changes in mass occur? a) double b) 9X
c) 6X
Section 5
What Do You See?
Things being measured in two different scenarios What Do You Think? Can you use the same scale to weight a canary and an elephant?
Yes, it wont be as precise. How does a bathroom scale work?
A bathroom scale works by measuring the force put on it, thus measuring your weight due to gravity. Physics Talk
Hooke's Law describes the force a spring exerts. The definition of Hooke's Law is the restoring force exerted by a spring is directly proportional to the distance of stretch or compression of the spring. The more you stretch a spring, the larger the restoring force of the spring. Force exerted by the string is equal to spring constant times spring stretch (Fs=kx). “K” is an indication of how easy or difficult it is to stretch or compress a spring. To find k you need to measure the force exerted by the spring and the stretch of the spring, it measures the stiffness of the spring. Many scales more by compressing a spring Checking up 1. A spring obeys Hooke’s law. If the force on the spring increased five times, how much does the stretch of the spring increase?
Five times 2. What is meant by the “spring constant” of a spring?
Measures the stiffness of the spring 3. How does the weight of an object in newtons compare to its mass in kilograms?
The greater the mass the greater the weight, this rule applies using Earth gravity. 4. When you stand on a bathroom scale how does the force of compression of the spring to your weight?
The more you weigh, the more the spring compresses Physics To Go 1. Calculate the weigh of the following objects
a) a football player with a mass of 100 kg
b) a toddler with a mass of 10kg
c)an adult with a mass of 60 kg 2. Use the approximation that the weight of a ¼-lb burger is one Newton. (Likewise, one stick of butter = ¼ lb butter has a weight of one newtons)Write down the approximate weight (in newtons) of the following objects: a) a 130-lb student
500 N b) a 1000-lb roller-coaster car
4000 N c) a 50-lb child
200 N 3. Weights were hung from a spring and the stretch of the spring was measured.
a) Graph the data with the stretch of the spring on the x-axis and the weight on the y-axis
b) If the data points do not fall exactly on a straight line, draw the best-fit line through the data points c) Find the slope of the graph
0.1482 d) What is the meaning of the slope?
Slope if the constant 4. A weight of 12 N causes a spring to stretch 3.0 cm. What is the spring constant (k) of the spring? 5. When Robert Hooke first described the relationship that has come to be known as Hooke’s law, he wrote “as the force, so the stretch.” Explain in a full sentence or two what Hooke meant by this
That mean as the force on the spring increases so does the stretch distance 6. Two springs have spring constants of 10.0 N/cm and 15.0 N/cm. Which spring is more difficult to stretch?
Spring with a constant of 15 N/cm 7. Calculate the spring constant (k) from the graph of a stretched spring below 0-3= 3/2 N/cm
0-2 8. To include the apparent weight changes in your design fro your roller coaster, you wil need to describe how a spring scale works. Write a brief description of how a spring scale works. Write a brief description of how a spring scale works.
A spring scale works by compressing as weight is put onto it. The more weight you add, the more the spring compresses.
Section 6
What Do You See?
People on fast moving elevator the one dropping has the man at no weight because he is not touching the scale and the one going up have the kid very heavy because the elevator is moving up. What Do You Think?
Yes an object in motion stays in motion law applies because sudden drop casue the cart to move but you to keep going the original way
Yes because you bounce due to accelerations and change in directions. Checking up 1. What is the sum of all the forces acting on an object when it is moving up a constant speed?
0 2. A person sitting on a bathroom scale on a roller coaster is accelerating upward. How does the reading on the bathroom scale compare to the person’s weight?
Greater 3. When you accelerate upward, why do you feel as if you weigh more?
An object at rest stays at rest so when its moved by an unbalanced force it is felt 4. Suppose you are standing on a bathroom scale in an elevator when the cable breaks. What does the bathroom scale read when you are falling with the elevator?
0 5. What is the force that slows a falling raindrop?
Air resistance What do you think now?
Weight never changes because mass and gravity never change. The net force is what effects the reading on a scale Physics Talk
Newton's first law says an object at rest has no net force acting on it the second law says an object at rest stays at rest. The same goes for an object in constant velocity. When accelerating up there is a net force pushing you up so your red of your actual weight changes to a higher number. Weight readings are identical when the elevator is in constant motion or at rest. When elevators accelerate down there is a smaller force than originally to the weight reads less then the actual weight. Air resistance can't be ignored on a roller coaster. Free fall has an acceleration 9.8. Physics To Go 1. Objects near the surface of Earth accelerate at a rate pf 9.8 m/s every second if gravity is the only significant force acting on them. Based on this information, how fast will an object be going after it has fallen from rest after each of the following lengths of time?
a)
b)
c) 2.Objects near the surface of the Moon accelerate at a rate of 1.6 m/s every seconod. Based on this information, how fast will an object be going after is has fallen from rest after each of the following lengths of time?
a)
b)
c) 4.
Motion of the Elevator
V, A, and ∑F (up, down, zero)
Relative Scale Reading (greater, less or equal to weight)
At rest, bottom floor
V= 0, a = 0, ∑F = 0
N = w
Starting at Rest, Increasing Up
V = up, A = Up, ∑F = up
N > w
Continuing to move, Constant Up
V = Up, A = 0, ∑F = 0
N = w
Slowing down to top floor, Decreasing Up
V = Up, A = Down, ∑F = Down
N < w
At rest, top floor
V= 0, A = 0, ∑F = 0
N = w
Starting at rest, Increasing Down
V = Down, A = Down, ∑F = Down
N < w
Continuing to move, Constant Down
V = Down, A = 0, ∑F = 0
N = w
Coming to a stop on the ground floor
V = Down, A = Up, ∑F = Up
N > w
5. At student weights 140 lb. On an elevator, the person is surprised to find that the scale only reads 137 lb for a few moments. Describe the motion of the elevator
Increasing down. 6. A person in an elevator at rest weighs 600 N. The elevator is about to move from the second floor to the fifth floor. When it firsts starts to move, what will the passenger observe about the weight indicate by a bathroom scale on which the passanger is standing?
Be greater 7. An elevator at the top floor begins to descend with an acceleration of 1.5 m/s^2. A person is standing on a bathroom scale in the elevator a) Will the bathroom scale’s reading increase or decrease once the elevator starts Decrease b) What will a bathroom scale read if a 50-kg person is standing on the scale during the acceleration? 8. A 50-kg student is on a scle in the elevator. a) What will be the scale reading when the elevator is at rest?
490 N. b) What will be the scale reading when the elevator accelerates up at a rate of 2m/s^2?
590 N. c) What will be the scale reading as the elevator travels up at a constant speed?
490 N. 9. Explain the meaning of the three sketches below. Specifically, why there a different scale reading for the same student in each elevator?
In the first picture the elevator is at rest/constant velocity so the scale is going to read 113 lb because that is Normal weight. In the second picture the elevator is in free fall. The reading on the scale is 0 because the person and elevator are traveling the same amount. In the third picture the elevator is accelerating upward so the reading on the scale is going to be greater. What Do You Think Now?
Your weight doesn’t change, your apparent weight does.
Yes.
Section 7
What do you see?
Speed increases and you want to go in a straight line and you need force to keep you on the track What do you think?
You don't fall out because your speed keeps you moving with the track Physics Plus
1. a) As the mass increases on the right side of the equation, then the right side of the equation gets larger. What happens to the net force? Describe in your log how this agrees with your observations. Net force becomes larger b) If velocity increases on the right side of the equation, what happens to the net force? Describe in your log how this agrees with your observations. Net force becomes larger 2. A roller coaster car going with twice the spee daroind a banked curve needs a stranger track. Write down in your log how much stronger the trck must be for a doubling of the speed
In this cause the track should be able to hold four times more force then it could before 3. If the radius of the curve increases on the right side of the equation, then the right side of the equation, the the right side of the equation gets smaller since the r is in the denominator of the fraction. What happens to the net force?
Net force gets smaller if the right side of the equation gets smaller 4. Complete the following sentence in your log The larger the radius for the curve, the smaller the force required to keep the car moving along the curve. If the curve is tight (r is very small) then a greater force is required 5.The limiting case of the large curve is where the curve's radius is so very large that the curve and a straight line are hardly distinguishable. On a straight path, no force is required. Describe in your log how this agrees with your observations of the stopper on a string.
The less curvy the curve is the less force is needed to keep the car moving Sample Problem A roller-coaster cart moving at 12.0 m/s enters a horizontal turn with a radius of curvature equal to 20.0m a) What is the centripetal acceleration of the roller coaster? b) If the mass of the passengers and car is 300 kg, what is the net centripetal force required to keep the car on its tracks?
Physics Talk
Circular motion/acceleration is ac=v^2/R. Centripetal force is Fc=mv^2/R. Mass and force have a direct relationship which means when mass increases so does the force
The velocity and force have a direct square relationship which means when velocity increases so does force. Net force always points to the center Checking up 1. What is required to make an object travel in a circle?
Centripetal Force 2. If you are traveling in a circle at constant speed, are you accelerating?
Yes, it takes force to keep you traveling at a constant speed 3. At the top of a roller-coaster loop, what two forces provide the centripetal force?
Normal Force 4. What force is responsible for your apparent weight a roller coaster?
Gravity 5. How does the centripetal force acting on an object depend upon the object’s mass? On the radius of the curve? On the object’s speed?
The larger the radius of the circle, the less force is required Physics To Go 1A battery-operated toy car is attached to a string a) If the loose end of the string is held to the ground, draw the path of the car while the battery is running b)If the string were to break while the car was moving in a circle, draw the path that the car would follow 2. Consider a real car on the road making a turn a)What force has replaced the string of the toy car in Question 1a?
Friction of the tires replaces the string of the car. b) If the car were to hit a section of ice, draw the path that the car probably would follow 6. A roller-coaster car is traveling east at 20 m/s. After 2s, it is travling north at 20m/s a) Did the speed of the roller-coaster car change?
No b) Did the velocity of the roller-coaster car change?
Yes c)What was the change in velocity of the roller-coaster car? Give both magnitude and direction for the change in velocity
45 degrees 7. A roller-coaster car is traveling east at 20m/s in circular path. After 16s, it is traveling north at 20m/s. The circular curve had a radius of 200m. Calculate the acceleration of the car and give its direction 10. Fill in the missing values in the tables that you created in your Active Physics log: a)
Required Fc (N)
Required Weight (N)
Normal Force (N)
top of the loop
4000
500
3500
bottom of the loop
6000
500
6500
b) Slow Moving
Required Fc (N)
Required Weight (N)
Normal Force (N)
top of the loop
800
500
300
bottom of loop
2800
500
3300
13. Use the diagram of the Terminator Express roller coaster. Indicate at which of the following points the passengers will feel heavy, where they will feel light, and where it is uncertain
a) heavier
b) uncertain
c) heavier
d) heavier
e) normal 14. Using the diagram of the Terminator Express, indicate at which of the following points the centripetal force is up, when it is down, when it is zero, and when it is sideways
a) up
b) down
c) up
d) up
e) zero What Do You Think Now?
The track has to provide lots of force to keep you in
Section 8
What Do You See?
Kids pulling a roller coaster to the top then riding it down What Do You Think? Physics Talk
W=Fd and displacement is parallel to the force. When an incline is steeper, more force is needed, but the distance along the incline is shorter. Work will always stay the same. Work is converted into GPE while going up an incline. Brakes or large springs can be used to stop the coaster. KE is transferred into EPE to stop the cart. Power is the work divided by the time. Power is measured in watts (J/s). Roller coasters usually use electrical energy, which is measured in voltage, to get up an incline. KE and GPE of a roller coaster are transferred to heat and sound energy as well. Checking Up 1. When a spring scale is used to do work pulling a cart to the top of an incline, where has the energy gone when the cart is at a rest at the top?
All to GPE. 2. Where does the roller coaster get its gravitational potential energy when it is at the top of the first hill?
From the work that the cart has while getting up the hill. 3. Why do truckers use a ramp when loading a truck if the wrk required is the same with or without a ramp?
They need less force for a longer distance. 4. When the brakes stop a roller coaster, what happens to the coaster’s kinetic energy?
The roller coaster's kinetic energy is transferred into work because of the friction. 5. What is the unit for power?
Watts. Physics To Go 1. A lab cart starts at the top of the incline. It slides down the incline a distance l and comes to rest copmressin a spring a distance x a) Compare the GPE of the cart at the top of the incline and at the bottom
The top has more GPE then the bottom b) How much work was done on the cart by the force of gravity (the cart’s weight) as the cart went from the top to the bottom
Work is the change in the GPE. c) How much work was done on the cart by the spring as the spring was compressed?
It is equal to the amount of work, which equals the GPE. d) What is the spring’s SPE when it is compressed by the distance x? e) Describe the total energy of the cart just before it hits the spring
KE and some GPE f) At which point does the cart begin to slow down?
When it first hits the spring 2. Calculate the work done in the following situations: a) A waiter applies a force of 150 N to hold a tray filled with plates on his shoulder. He ten moves 7 m toward the kitchen door. What is the work done on the tray by the waiter?
The work is zero because the force and distance are perpendicular. b) A bowler lifts a 60-N bowling ball from the rack to his chest, a vertical ditance pf .5 m. What is the work done on the bowling ball by the bower? c) A girl pulls her sled up a hill. The length of the hill is 40 m and the pulling force required was 75 N. What is the work done by the firl on the sled if she pulls the rop on the sled while the string is parallel to the hill? d) The weight of a dumbbell is 500 N. It is lifted over a body-builder’s head, a distance of .7 m. What is the work done by the body-builder on the dumbbell? 3. Why are you told conserve energy if the conservation of energy tells you that energy is always conserved? Create a better way of saying “conserve energy.”
Don't waste energy 4. If you were to fill the lab cart you used in the Investigate with clay to represent the people in the roller coaster, what would have changed in the experiment?
Mass would increase 5. An electric motor lifts a roller-caoster car that weights 10,000 N to the top of the first hills that is 20 m above the ground. To add suspense, the ride up takes 150 s
a)
b) 6. In the terminator Express roller coaster, describe one trip of the coaster car around the ramp in terms of work and energy
GPE increases and work is done. At the top, all is GPE. Going down, you change from GPE to KE. At the bottom of the first hill, you have mostly KE. At the top a vertical loop, you have GPE and KE. At the bottom of the loop, you have KE. At the back curve, you have KE and some GPE depending on height. Then in horizontal loop, you have KE. At the breaking ramp, work is done to stop you due to friction. What Do You Think Now?
If they are going the same distance then they require the same amount is used
Section 9
What Do You See? A girl thinking about energy and writing things down and there is boy is thinking about force and seems to not have anything written down and is having a hard time What Do You Think? Which parts of The Snake will be the most thrilling? When movement occurs If the speed of The Snake always remains the same, why will it still be fun? It is still fun because of the constant changes. Physics Talk A number with both a number and direction is called a vector. A number with magnitude and no direction is a scalar. Displacement is taken into account only with vectors. Energy is a scalar. The total mechanical energy (KE + GPE) is equal at all points of the roller coaster (ignoring friction). Force is a vector quantity. Normal force is always perpendicular to the track. The changes in acceleration, size, and direction create the thrills. Force and energy are related. Force in the direction of motion creates work energy and any work done creates changes in energy. In order to have a net force, there needs to be some type of acceleration. Checking Up 1. What process is needed to add vector quantities? The Pythagorean theorem. 2. Is energy a vector or a scalar? Is force a vector or a scalar? Scalar. Vector. 3. For roller coasters, what three things do energy considerations tell you about the coaster at different points? GPE and KE are equal at all points of the coaster that are the same height. 4. Does the energy of the roller coaster depend upon the path the roller coaster takes? Energy considerations are path independent 5. What is required to provide a change in the energy of a roller coaster? Work is a force applied over distance. Physics To Go 1. A roller coaster makes a sharp right turn. The velocity of the roller coaster car is 5.0 m/s south before the turn and 5.0 m/s west after the turn a) Determine the change in velocity of the roller coaster cart using vector diagram b) Determine the change in velocity of the roller coaster cart using the Pythagorean theorem. You can figure out the angle in case from the vector diagram 2. All roller coasters that begin at the same height have the same speeds at the bottom. Explain why these two roller-coaster tracks provide the same change in speed when a cart goes from the top to the bottom. GPEs are equal so then GPE goes down the KE goes up it is all equal. 3. Identify the following as vectors or scalars a) scalar b) vector c) scalar d) vector e) vector f) vector g) scalar h) scalar i) scalar 4. Which of the following statements are about vectors and which are about scalars? a) scalar b) vector c) scalar d) vector 5. Sometimes it is easier to look at a roller coaster as an energy ride, while other times it is best to look at a roller coaster as a force ride. Give an example of each approach. As an energy ride, it is easier when you are trying to find speeds, know the heights. It isn't useful when trying to find accelerations for energy. 6. a) Draw the forces acting on roller coaster 1 at appoints A, B,C, and D b) Draw the forces acting on roller coaster 2 at points A,B, C, D c) Why is it easier to use forces at analyze roller coaster 2? The forces are the same everywhere. 7. a) Label three points on roller coaster 3 that have the same GPE/ b) Compare the total energies of the roller coaster at these points They are equal. c) Compare the KE of the roller coaster at these points They are the same because velocity is practically the same. d) Why are you able to ignore the other points of the roller coaster when compareing the GPE and KE and total energy? At all points, the GPE plus the KE are equal.
Section 10
What Do You See?
A terrible roller coaster with people dieing What Do You Think?
Does the knowledge that people can get hurt or die on a roller coaster change the thrill of the ride?
Yes, but if it is a small change it feels exciting, if its a large change I wouldn't go on it
Would your answer change if you found out that one-half of all roller-coaster rides in the death of its passengers?
I would never go on. Physics Talk
Max. acceleration in a curve = 4gs =39.2 m/s ^2. Ac=v^2/r. If Ac is greater then 39.2 change the radius to be greater. You can also decrease speed by decreasing initial height or increase the height of the curve itself.
Forces and apparent weight. a=4g and N= 5g at the bottom of a loop. If you have a=4g and N=3g at the top of a loop
Min. Speed Required at Top of a Loop. Acceleration needs to be greater then 9.8 Checking Up 1. What is the maximum safe acceleration fro a roller coaster? 4 g's. 2. List two ways to keep acceleration of coaster cart low enough to be safe. Decrease speed and increase of radius 3. At what part of the loop is the greatest on a roller coaster cart? The bottom 4. At what part of the loop is the normal force the greatest The bottom Physics To Go 1. An engineering company submits a plan for a roller coaster. Make sure it is always under 4g's. Able to obtain the mass of the people. You also must have enough speed to make it around the loop 2. A roller-coaster car is traveling at 20.0 m/s at the bottom of a loop. The radius of the loops is 12.0m. a) Using the conversation of mechanical energy, calculate the initial height of a roller-coaster car when it starts from rest to give it a speed 0f 20.0 m/s the bottom of a loop b) Using the equation a=v^2/r, calculate the acceleration at the bottom of the loop. c) Is this a safe acceleration? Yes d) At what speed would this loop with radius of 12.0 m begin to be a safety concern? Yes e) At what speed would the acceleration in a loop with smaller radius of 7.0 m begin to be a safety concern? Yes 3. A roller-coaster car is traveling at 25.0 m/s at the bottom of a loop. The radius of the loop is 10.0 m. a) Calculate the acceleration of the car at the bottom of the loop. b) Is this a safe acceleration? This isn't safe because it is greater than 4. 4. A roller coaster has an initial height of 50.0 above the bottom of an incline. a) What will the speed of the roller-coaster car at the bottom of the incline? b) The roller-coaster car goes into a loop with a radius of 10.0 m. What is the acceleration required to keep the cart moving in the circular loop? c) What will be the speed of the roller-coaster car at the top of the loop? e) Explain whether this roller coaster is safe at the bottom and the top of the loop The acceleration is safe at the top and the bottom of the loop. 6. A roller-coaster car, when filled with people, has a mass of 900.0kg. The roller-coaster car rounds a curve on the ground with a radius of 18.0 m at a speed of 12.0 m/s a) What is the centripetal acceleration of the car? b) What is the centripetal force on the car? c) What will provide the centripetal force? Track on wheels 7. A roller-coaster car, when filled with people has a mass of 900.0 kg. The roller-coaster cart rounds a curve on the group with a radius of 15.0 m at a speed of 20.0 m/s. a) What is the centripetal acceleration of the car? b) What is the centripetal force on the car? c) The wheels in the tracks can provide a force of 25,000 N. Is the roller coaster safe? Yes because the Fc is 24,000 and the wheel have 25,000 N 8. A roller coaster is able to complete a loop when the car has two passengers. The car is loaded with six people a) Will the centripetal acceleration change as a result of the change in mass? No because mass is not a factor b) Will the roller coaster be going faster, slower, or the same speed at the bottom of the loop with the extra passengers? The same speed c) Will the roller-coaster track require a stronger material because of the increased number of riders? Yes because the normal force from the track will need to be greater because weight is increasing.
Megan Lynch's Wikilog - Period 8 CP Physics - E. Burns - 2010
Table of Contents
Section 1
What Do You See?A boy pretending he is on a rollarcoaster by having someone push him blindfolded on a rolling chair
What Do You Think?
Which part of the roller-coaster ride produces the loudest screams? Why?
The speed and the loops produce the loudest screams because it is exciting and scary
Homework 3-28-11
El Toro
- The track is made so that it snaps together like Lego pieces and is made of more layers of wood that are tightly bonded together instead of nailed together by hand like a traditional wooden roller coaster.
- Constant speed
GoliathChecking Up
1. Explain the difference between distance and displacement.
Displacement has magnitude and direction and distance has direction.
2. You went to school and back home, a total distance of 2km. What is your displacement?
3.What is the difference between speed and velocity?
Velocity has a direction and speed doesn’t
4. How can you find the acceleration of an object?
By using its change in velocity and its time. Then you do v/t to find the acceleration.
Physics to Go
1.
The drops and the horizontal loop because they have the change in acceleration and direction that makes the ride exciting
3. Speed by itself does not produce thrills. Living on Earth, you already have a big speed, since Earth is constantly turning
a) Earth makes a complete revolution once every 24h. La Paz, Bolivia is close to the Equator and travels a large circumference in 24h. Oslo, Norway is close to the Arctic Circle and travels a smaller circumference in 24 h. Which city has the greater speed?
Bolivia
b) The circumference of Earth’s Equator is about 40,000 km. It requires one day or 24 h to complete one revolution. Calculate the speed you are traveling on Earth if you are at the Equator
Ch4_S1_PTG3b.png
c) Why do you not get a big thrill going at such a high speed?Because there is no acceleration happening
4. A roller-coaster rider traveling in a straight line changes from a speed of 4 m/s to 16 m/s in 3 s. Calculate the acceleration of the ride.
Ch4_S1_PTG4.png
5. Identify the following situations as an example of either distance, displacement, speed, velocity, or acceleration.a) a car traveling at 50km/h
Speed
b) a student riding a bike at 4m/s toward home
Velocity
c) a roller-coaster ride whips around a left turn at 5m/s
Acceleration
d) a roller-coaster car is dragged up a hills 12 m tall traveling at 3m/s.
Displacement and Velocity
e) a train ride takes you 150 km northeast
Displacement
6. A lab cart is 10 cm long. It travels through a velocimeter in 2 s. Calculate the cart’s speed.
Ch4_S1_PTG6.png
7. A second lab cart is 5 cm long. If it were traveling at the same speed as the casrt in Question 6, what would the velocimeter record as the elapsed time?
Ch4_S1_PTG7.png
8. Your vehicle accelerates from 0 to 25 m/s (about 55mi/h) in 10 s while traveling down a straight street. What is the acceleration of your vehicle?
Ch4_S1_PTG8.png
What do you think now?I think that drops, loops, and change in acceleration will have provide the excitement because they are the unexpected
Section 2
What Do You See?People are having fun on the downhill and the staright slow parts they are bored
What Do You Think?
The 90 angle one because it is a larger angle
Physics Talk
The initial height of the ball is determined by the height of where the ball starts. KE and GPE depend on the mass of the ball. As the ball comes down the incline the GPE decreases and the KE increases
Checking Up
1. What effect does changing the length of the incline have on the speed of a ball when it rolls to the bottom?
It had no effect on the speed of the ball
2. How does the gravitational potential energy of an object change with its height? With its mass?
As the height goes up the GPE goes up. The mass goes up the GPE goes up also.
3. How does the kinetic energy of an object change with its speed? With its mass?
As the speed goes the up KE goes up. The mass goes up as the KE goes up also.
4. As a roller-coaster car rolls down a hill, what happens to the gravitational potential energy it loses?
Its put into KE
5. If a roller-coaster car has 40,000 J of GPE when at rest on the top of a hills how much KE does it have when it ¾ of the way down the hills
30,000
Physics To Go
1. For which track is the speed of the car greatest at the bottom?
They are the same
3. Mass of car = 200kg g = 10m/s^2
Mass of car = 300kg and g = 10m/s^2
7. A pendulum is lifted to a height of .75 m. The mass of the bob is .2 kg.
a) Calculate the GPE at the top.
b) Find the KE of the bob at the bottom
c) At what position of the bob will the GPE and KE be equal
The middle
8. In the early morning, a roller-coaster train (set of cars hookes together) only has 6 passengers. In the afternoon it has 26 passenger. Will the sppeed of the roller coaster change with more passengers aboard? Explain your answer
It would not change because GPE and Ke both have mass so they cancel eacho ther out making irrelevant
9. To the right is a side view of a roller coaster that starts from rest at position A.
a)At which point is the roller-coaster car traveling the fastest? Explain.
From A-B because it is accelerating the most
b) At which two points is the roller-coaster car traveling at the speed? Explain.
B and G because they are both changing direction
c) Is the roller coaster car traveling faster at E or D? Explain.
D because it has finished accelerating
10. Above and to the right is a side view of a roller coaster that starts from rest at position A
b) Why can’t the roller coaster each point H
Because it does not have enough KE to get itself up the hill
They will be the same speed because they are both starting at the same height. Roller coaster B will provide the most thrills because it is steep.
Section 3
What Do You See?Students measuring how far a frog bouncy toy goes with a meter stick and a photogate timer
What Do You Think?
How does the roller coaster today get up to its highest point?
They are now motorized
Does it cost more to lift the roller coaster if it full of people?
No
Physics talk
Spring potential energy (EPE) is the energy stored in a spring due to its compression or stretch. The equation is EPE= 1/2kx2.
Checking up
1. What happens to the spring potential energy of a “pop-ip” toy after it leaps off the table
EPE would turn into KE upon flight
2. A ”pop-up” toy had 2J of spring potential energy before popping. How much kinetic energy will the toy have just after leaving the table
2J
3. A “pop-up” toy has 2J of spring potential energy before popping. How much gravitational potential energy will it have at the top?
2J
4. What two factors determine the amount of spring potential energy that is stored in a psring
The distance it is compressed and its constant (k)
Physics To Go
5. Why can the second hill of the roller coaster not be higher than the girst hill?
The amount of KE needed to get over the second hill cannot be larger then the amount needed for the first.
6. Why does the roller coaster not continue forever and go back and forth and up and down the hills over and over again?
There is work and friction that slows the roller coaster
7. A roller coaster of mass 300 kg ascends to a hright of 15m. How much electrical energy was required to raise the cars to this height?
8.A roller-coaster car has a mass of 400kg and a speed of 15m/s
a)What is the KE of the roller-coaster car?
b)What will be the GPE of this roller-coaster car at its highest point, where KE=0 at that point
45,000J
c)How high can the roller-coaster car go with this much energy?
9. A bal is thrown upward from Earth’s surface. While the ball is rising, is its gravitational potential energy increasing, decreasing, or remaining the same?
It is increasing, as h increases GPE increases
10. Three people of equal mass climb a mountain using paths A, B, and C shown in the diagram. Along which path(s) does a person gain the greatest amount of GPE from start to finish.: A only, B only, C only, or is the gain the same along all paths
They all reach the same end point and reach the same GPE
11. In an experiment similar to your toy, the mass of the spring toy was 0.020 kg. The height that the toy rose to was 0.40 m. The initial speed of the spring toy as measured by the velocimeter was 2.7m/s.
a)Do the GPE and the KE both give approximately the same values?
b) What is the EPE before the toy pops
0.13 m
12. A roller coaster begins at a height of 18 m. The mass of the roller coaster and passengers is 300 kg. When the roller coaster reaches the bottom, its brakes fail. An emergency spring must bring the coaster to rest
a) What must be the spring constant of this spring if it will be compressed by 4m?
6600 N/m
b) How much will the spring compress if an additional 100 kg of people are aboard?
4.62m
13. An umbrella has an automatic opening mechanism. When the umbrella is closed, a spring is compressed. The spring constant is 40 N/m and the spring is compressed 0.3m. What is the KE of the umbrella when it begins to open?
Section 4
What do you see?The more gravity a roller coaster has the faster you go.
What do you think?
Gravity has a direction to the Earth's crust. Australia can be held on Earth because they are being pushed towards the core.
Physics Talk
Earth's gravitational Field is the gravitational influence in the space around a massive object. It needs a source of the field and a second object to interact with the field, the response object. Gravitational field lines show the direction of the gravitational field, that the field is stronger where the lines are close together and weaker where the lines are further apart, some points of the field and that the field extends to infinity. Inverse-Square Relationship is the relationship between the magnitude of a gravitational foe and the distance from the mass. It also describes how electrostatic forces depend on the distance from an electrical charge. Newton's law of universal gravitation is that all bodies with mass attract all other bodies with mass. The force is proportional to the product of the two masses and gets stronger as either mass gets larger. Gravity is the force of attraction between two bodies due to their masses. The Universal Gravitation equation is
Checking up
1. What is the direction of the gravitational field in your classroom?
The direction of the strongest gravitational field is to the center of the earth.
2. Using the idea of field lines, where is the gravitational field the strongest?
The closer you are to an object, the stronger the field.
3. If you triple the distance between two masses, what happens to the force gravity between the two masses?
You divide it by 9
4. What is the force that holds the Moon in its orbit around Earth?
Gravity
5. Approximately white is the shape of the orbit of the planets around the Sun?
Circular
Physics To Go
1. The gravitational force beween two asteroids is 500 N. What would the force be if the distance between them doubled?
250N
3. Why does everyone trust in gravity
We have always believed in it and there is no reason not to
4. Compare the acceleration due to gravity at the top and bottom of a roller-coaster ride.
They are equal
5. a) Which is closer to the Moon- the middle of Earth or the water on the side of Earth facing the Moon ?
The water on the side of the earth facing the moon
b) Suggest an explanation for high tides on the side of Earth facing the Moon.
Only the water is effected by the gravity of the moon because it is weaker then the Earth’s.
c) Use your answer to a) to propose an explanation for the uneven distribution of water on Earth’s surface, as shown in the diagram
The force of gravity is stronger when the moon and the water get closer
6. Astronauts on many Shuttle fligts study the effects of “free fall.” Fish taken aboard the Shuttle react to “free fall” by swimming in circles. “Free fall” minics what you feel if gravity were not present
a) How would a fish’s life be different without gravity
They would die because there wouldn't be a body of water for them to live in
b) Does gravity hold a fish “down” on Earth?
Yes
7. Two objects have a tiny, but measurable gravitational force of attraction between them. How will that force change if the distance between the objects is
a) divided by 4
b) divided by 9
c) divided by 16
d) multiplied by 4
8. Two objects have a tiny, but measurable gravitational force of attraction between them. How will that force change if the mass of one of the objects is
a) divided by 4
b) divided by 9
c) divided by 16
d) multiplied by 4
9. Two objects have a tin, but measurable gravitational force of attraction between them. How will that force change if the mass of both of the objects is
a) doubled
b) tripled
c) quadrupled
d) halved
10. Two objects have a tin, but measurable gravitational force of attraction between them. How will that force change if the following changes in mass occur?
a) double
b) 9X
c) 6X
Section 5
What Do You See?Things being measured in two different scenarios
What Do You Think?
Can you use the same scale to weight a canary and an elephant?
Yes, it wont be as precise.
How does a bathroom scale work?
A bathroom scale works by measuring the force put on it, thus measuring your weight due to gravity.
Physics Talk
Hooke's Law describes the force a spring exerts. The definition of Hooke's Law is the restoring force exerted by a spring is directly proportional to the distance of stretch or compression of the spring. The more you stretch a spring, the larger the restoring force of the spring. Force exerted by the string is equal to spring constant times spring stretch (Fs=kx). “K” is an indication of how easy or difficult it is to stretch or compress a spring. To find k you need to measure the force exerted by the spring and the stretch of the spring, it measures the stiffness of the spring. Many scales more by compressing a spring
Checking up
1. A spring obeys Hooke’s law. If the force on the spring increased five times, how much does the stretch of the spring increase?
Five times
2. What is meant by the “spring constant” of a spring?
Measures the stiffness of the spring
3. How does the weight of an object in newtons compare to its mass in kilograms?
The greater the mass the greater the weight, this rule applies using Earth gravity.
4. When you stand on a bathroom scale how does the force of compression of the spring to your weight?
The more you weigh, the more the spring compresses
Physics To Go
1. Calculate the weigh of the following objects
a) a football player with a mass of 100 kg
b) a toddler with a mass of 10kg
c)an adult with a mass of 60 kg
2. Use the approximation that the weight of a ¼-lb burger is one Newton. (Likewise, one stick of butter = ¼ lb butter has a weight of one newtons)Write down the approximate weight (in newtons) of the following objects:
a) a 130-lb student
500 N
b) a 1000-lb roller-coaster car
4000 N
c) a 50-lb child
200 N
3. Weights were hung from a spring and the stretch of the spring was measured.
a) Graph the data with the stretch of the spring on the x-axis and the weight on the y-axis
b) If the data points do not fall exactly on a straight line, draw the best-fit line through the data points
c) Find the slope of the graph
0.1482
d) What is the meaning of the slope?
Slope if the constant
4. A weight of 12 N causes a spring to stretch 3.0 cm. What is the spring constant (k) of the spring?
5. When Robert Hooke first described the relationship that has come to be known as Hooke’s law, he wrote “as the force, so the stretch.” Explain in a full sentence or two what Hooke meant by this
That mean as the force on the spring increases so does the stretch distance
6. Two springs have spring constants of 10.0 N/cm and 15.0 N/cm. Which spring is more difficult to stretch?
Spring with a constant of 15 N/cm
7. Calculate the spring constant (k) from the graph of a stretched spring below
0-3= 3/2 N/cm
0-2
8. To include the apparent weight changes in your design fro your roller coaster, you wil need to describe how a spring scale works. Write a brief description of how a spring scale works. Write a brief description of how a spring scale works.
A spring scale works by compressing as weight is put onto it. The more weight you add, the more the spring compresses.
Section 6
What Do You See?People on fast moving elevator the one dropping has the man at no weight because he is not touching the scale and the one going up have the kid very heavy because the elevator is moving up.
What Do You Think?
Yes an object in motion stays in motion law applies because sudden drop casue the cart to move but you to keep going the original way
Yes because you bounce due to accelerations and change in directions.
Checking up
1. What is the sum of all the forces acting on an object when it is moving up a constant speed?
0
2. A person sitting on a bathroom scale on a roller coaster is accelerating upward. How does the reading on the bathroom scale compare to the person’s weight?
Greater
3. When you accelerate upward, why do you feel as if you weigh more?
An object at rest stays at rest so when its moved by an unbalanced force it is felt
4. Suppose you are standing on a bathroom scale in an elevator when the cable breaks. What does the bathroom scale read when you are falling with the elevator?
0
5. What is the force that slows a falling raindrop?
Air resistance
What do you think now?
Weight never changes because mass and gravity never change. The net force is what effects the reading on a scale
Physics Talk
Newton's first law says an object at rest has no net force acting on it the second law says an object at rest stays at rest. The same goes for an object in constant velocity. When accelerating up there is a net force pushing you up so your red of your actual weight changes to a higher number. Weight readings are identical when the elevator is in constant motion or at rest. When elevators accelerate down there is a smaller force than originally to the weight reads less then the actual weight. Air resistance can't be ignored on a roller coaster. Free fall has an acceleration 9.8.
Physics To Go
1. Objects near the surface of Earth accelerate at a rate pf 9.8 m/s every second if gravity is the only significant force acting on them. Based on this information, how fast will an object be going after it has fallen from rest after each of the following lengths of time?
a)
b)
c)
2.Objects near the surface of the Moon accelerate at a rate of 1.6 m/s every seconod. Based on this information, how fast will an object be going after is has fallen from rest after each of the following lengths of time?
a)
b)
c)
4.
Increasing down.
6. A person in an elevator at rest weighs 600 N. The elevator is about to move from the second floor to the fifth floor. When it firsts starts to move, what will the passenger observe about the weight indicate by a bathroom scale on which the passanger is standing?
Be greater
7. An elevator at the top floor begins to descend with an acceleration of 1.5 m/s^2. A person is standing on a bathroom scale in the elevator
a) Will the bathroom scale’s reading increase or decrease once the elevator starts
Decrease
b) What will a bathroom scale read if a 50-kg person is standing on the scale during the acceleration?
8. A 50-kg student is on a scle in the elevator.
a) What will be the scale reading when the elevator is at rest?
490 N.
b) What will be the scale reading when the elevator accelerates up at a rate of 2m/s^2?
590 N.
c) What will be the scale reading as the elevator travels up at a constant speed?
490 N.
9. Explain the meaning of the three sketches below. Specifically, why there a different scale reading for the same student in each elevator?
In the first picture the elevator is at rest/constant velocity so the scale is going to read 113 lb because that is Normal weight. In the second picture the elevator is in free fall. The reading on the scale is 0 because the person and elevator are traveling the same amount. In the third picture the elevator is accelerating upward so the reading on the scale is going to be greater.
What Do You Think Now?
Your weight doesn’t change, your apparent weight does.
Yes.
Section 7
What do you see?Speed increases and you want to go in a straight line and you need force to keep you on the track
What do you think?
You don't fall out because your speed keeps you moving with the track
Physics Plus
1.
a) As the mass increases on the right side of the equation, then the right side of the equation gets larger. What happens to the net force? Describe in your log how this agrees with your observations.
b) If velocity increases on the right side of the equation, what happens to the net force? Describe in your log how this agrees with your observations.
2. A roller coaster car going with twice the spee daroind a banked curve needs a stranger track. Write down in your log how much stronger the trck must be for a doubling of the speed
In this cause the track should be able to hold four times more force then it could before
3. If the radius of the curve increases on the right side of the equation, then the right side of the equation, the the right side of the equation gets smaller since the r is in the denominator of the fraction. What happens to the net force?
Net force gets smaller if the right side of the equation gets smaller
4. Complete the following sentence in your log The larger the radius for the curve, the smaller the force required to keep the car moving along the curve. If the curve is tight (r is very small) then a greater force is required
5.The limiting case of the large curve is where the curve's radius is so very large that the curve and a straight line are hardly distinguishable. On a straight path, no force is required. Describe in your log how this agrees with your observations of the stopper on a string.
The less curvy the curve is the less force is needed to keep the car moving
Sample Problem
A roller-coaster cart moving at 12.0 m/s enters a horizontal turn with a radius of curvature equal to 20.0m
a) What is the centripetal acceleration of the roller coaster?
b) If the mass of the passengers and car is 300 kg, what is the net centripetal force required to keep the car on its tracks?
Physics Talk
Circular motion/acceleration is ac=v^2/R. Centripetal force is Fc=mv^2/R. Mass and force have a direct relationship which means when mass increases so does the force
The velocity and force have a direct square relationship which means when velocity increases so does force. Net force always points to the center
Checking up
1. What is required to make an object travel in a circle?
Centripetal Force
2. If you are traveling in a circle at constant speed, are you accelerating?
Yes, it takes force to keep you traveling at a constant speed
3. At the top of a roller-coaster loop, what two forces provide the centripetal force?
Normal Force
4. What force is responsible for your apparent weight a roller coaster?
Gravity
5. How does the centripetal force acting on an object depend upon the object’s mass? On the radius of the curve? On the object’s speed?
The larger the radius of the circle, the less force is required
Physics To Go
1A battery-operated toy car is attached to a string
a) If the loose end of the string is held to the ground, draw the path of the car while the battery is running
b)If the string were to break while the car was moving in a circle, draw the path that the car would follow
2. Consider a real car on the road making a turn
a)What force has replaced the string of the toy car in Question 1a?
Friction of the tires replaces the string of the car.
b) If the car were to hit a section of ice, draw the path that the car probably would follow
6. A roller-coaster car is traveling east at 20 m/s. After 2s, it is travling north at 20m/s
a) Did the speed of the roller-coaster car change?
No
b) Did the velocity of the roller-coaster car change?
Yes
c)What was the change in velocity of the roller-coaster car? Give both magnitude and direction for the change in velocity
45 degrees
7. A roller-coaster car is traveling east at 20m/s in circular path. After 16s, it is traveling north at 20m/s. The circular curve had a radius of 200m. Calculate the acceleration of the car and give its direction
10. Fill in the missing values in the tables that you created in your Active Physics log:
a)
a) heavier
b) uncertain
c) heavier
d) heavier
e) normal
14. Using the diagram of the Terminator Express, indicate at which of the following points the centripetal force is up, when it is down, when it is zero, and when it is sideways
a) up
b) down
c) up
d) up
e) zero
What Do You Think Now?
The track has to provide lots of force to keep you in
Section 8
What Do You See?Kids pulling a roller coaster to the top then riding it down
What Do You Think?
Physics Talk
W=Fd and displacement is parallel to the force. When an incline is steeper, more force is needed, but the distance along the incline is shorter. Work will always stay the same. Work is converted into GPE while going up an incline. Brakes or large springs can be used to stop the coaster. KE is transferred into EPE to stop the cart. Power is the work divided by the time. Power is measured in watts (J/s). Roller coasters usually use electrical energy, which is measured in voltage, to get up an incline. KE and GPE of a roller coaster are transferred to heat and sound energy as well.
Checking Up
1. When a spring scale is used to do work pulling a cart to the top of an incline, where has the energy gone when the cart is at a rest at the top?
All to GPE.
2. Where does the roller coaster get its gravitational potential energy when it is at the top of the first hill?
From the work that the cart has while getting up the hill.
3. Why do truckers use a ramp when loading a truck if the wrk required is the same with or without a ramp?
They need less force for a longer distance.
4. When the brakes stop a roller coaster, what happens to the coaster’s kinetic energy?
The roller coaster's kinetic energy is transferred into work because of the friction.
5. What is the unit for power?
Watts.
Physics To Go
1. A lab cart starts at the top of the incline. It slides down the incline a distance l and comes to rest copmressin a spring a distance x
a) Compare the GPE of the cart at the top of the incline and at the bottom
The top has more GPE then the bottom
b) How much work was done on the cart by the force of gravity (the cart’s weight) as the cart went from the top to the bottom
Work is the change in the GPE.
c) How much work was done on the cart by the spring as the spring was compressed?
It is equal to the amount of work, which equals the GPE.
d) What is the spring’s SPE when it is compressed by the distance x?
e) Describe the total energy of the cart just before it hits the spring
KE and some GPE
f) At which point does the cart begin to slow down?
When it first hits the spring
2. Calculate the work done in the following situations:
a) A waiter applies a force of 150 N to hold a tray filled with plates on his shoulder. He ten moves 7 m toward the kitchen door. What is the work done on the tray by the waiter?
The work is zero because the force and distance are perpendicular.
b) A bowler lifts a 60-N bowling ball from the rack to his chest, a vertical ditance pf .5 m. What is the work done on the bowling ball by the bower?
c) A girl pulls her sled up a hill. The length of the hill is 40 m and the pulling force required was 75 N. What is the work done by the firl on the sled if she pulls the rop on the sled while the string is parallel to the hill?
d) The weight of a dumbbell is 500 N. It is lifted over a body-builder’s head, a distance of .7 m. What is the work done by the body-builder on the dumbbell?
3. Why are you told conserve energy if the conservation of energy tells you that energy is always conserved? Create a better way of saying “conserve energy.”
Don't waste energy
4. If you were to fill the lab cart you used in the Investigate with clay to represent the people in the roller coaster, what would have changed in the experiment?
Mass would increase
5. An electric motor lifts a roller-caoster car that weights 10,000 N to the top of the first hills that is 20 m above the ground. To add suspense, the ride up takes 150 s
a)
b)
6. In the terminator Express roller coaster, describe one trip of the coaster car around the ramp in terms of work and energy
GPE increases and work is done. At the top, all is GPE. Going down, you change from GPE to KE. At the bottom of the first hill, you have mostly KE. At the top a vertical loop, you have GPE and KE. At the bottom of the loop, you have KE. At the back curve, you have KE and some GPE depending on height. Then in horizontal loop, you have KE. At the breaking ramp, work is done to stop you due to friction.
What Do You Think Now?
If they are going the same distance then they require the same amount is used
Section 9
What Do You See?A girl thinking about energy and writing things down and there is boy is thinking about force and seems to not have anything written down and is having a hard time
What Do You Think?
Which parts of The Snake will be the most thrilling?
When movement occurs
If the speed of The Snake always remains the same, why will it still be fun?
It is still fun because of the constant changes.
Physics Talk
A number with both a number and direction is called a vector. A number with magnitude and no direction is a scalar. Displacement is taken into account only with vectors. Energy is a scalar. The total mechanical energy (KE + GPE) is equal at all points of the roller coaster (ignoring friction). Force is a vector quantity. Normal force is always perpendicular to the track. The changes in acceleration, size, and direction create the thrills. Force and energy are related. Force in the direction of motion creates work energy and any work done creates changes in energy. In order to have a net force, there needs to be some type of acceleration.
Checking Up
1. What process is needed to add vector quantities?
The Pythagorean theorem.
2. Is energy a vector or a scalar? Is force a vector or a scalar?
Scalar. Vector.
3. For roller coasters, what three things do energy considerations tell you about the coaster at different points?
GPE and KE are equal at all points of the coaster that are the same height.
4. Does the energy of the roller coaster depend upon the path the roller coaster takes?
Energy considerations are path independent
5. What is required to provide a change in the energy of a roller coaster?
Work is a force applied over distance.
Physics To Go
1. A roller coaster makes a sharp right turn. The velocity of the roller coaster car is 5.0 m/s south before the turn and 5.0 m/s west after the turn
a) Determine the change in velocity of the roller coaster cart using vector diagram
b) Determine the change in velocity of the roller coaster cart using the Pythagorean theorem. You can figure out the angle in case from the vector diagram
2. All roller coasters that begin at the same height have the same speeds at the bottom. Explain why these two roller-coaster tracks provide the same change in speed when a cart goes from the top to the bottom.
GPEs are equal so then GPE goes down the KE goes up it is all equal.
3. Identify the following as vectors or scalars
a) scalar
b) vector
c) scalar
d) vector
e) vector
f) vector
g) scalar
h) scalar
i) scalar
4. Which of the following statements are about vectors and which are about scalars?
a) scalar
b) vector
c) scalar
d) vector
5. Sometimes it is easier to look at a roller coaster as an energy ride, while other times it is best to look at a roller coaster as a force ride. Give an example of each approach.
As an energy ride, it is easier when you are trying to find speeds, know the heights. It isn't useful when trying to find accelerations for energy.
6.
a) Draw the forces acting on roller coaster 1 at appoints A, B,C, and D
b) Draw the forces acting on roller coaster 2 at points A,B, C, D
c) Why is it easier to use forces at analyze roller coaster 2?
The forces are the same everywhere.
7.
a) Label three points on roller coaster 3 that have the same GPE/
b) Compare the total energies of the roller coaster at these points
They are equal.
c) Compare the KE of the roller coaster at these points
They are the same because velocity is practically the same.
d) Why are you able to ignore the other points of the roller coaster when compareing the GPE and KE and total energy?
At all points, the GPE plus the KE are equal.
Section 10
What Do You See?A terrible roller coaster with people dieing
What Do You Think?
Does the knowledge that people can get hurt or die on a roller coaster change the thrill of the ride?
Yes, but if it is a small change it feels exciting, if its a large change I wouldn't go on it
Would your answer change if you found out that one-half of all roller-coaster rides in the death of its passengers?
I would never go on.
Physics Talk
Max. acceleration in a curve = 4gs =39.2 m/s ^2. Ac=v^2/r. If Ac is greater then 39.2 change the radius to be greater. You can also decrease speed by decreasing initial height or increase the height of the curve itself.
Forces and apparent weight. a=4g and N= 5g at the bottom of a loop. If you have a=4g and N=3g at the top of a loop
Min. Speed Required at Top of a Loop. Acceleration needs to be greater then 9.8
Checking Up
1. What is the maximum safe acceleration fro a roller coaster?
4 g's.
2. List two ways to keep acceleration of coaster cart low enough to be safe.
Decrease speed and increase of radius
3. At what part of the loop is the greatest on a roller coaster cart?
The bottom
4. At what part of the loop is the normal force the greatest
The bottom
Physics To Go
1. An engineering company submits a plan for a roller coaster.
Make sure it is always under 4g's. Able to obtain the mass of the people. You also must have enough speed to make it around the loop
2. A roller-coaster car is traveling at 20.0 m/s at the bottom of a loop. The radius of the loops is 12.0m.
a) Using the conversation of mechanical energy, calculate the initial height of a roller-coaster car when it starts from rest to give it a speed 0f 20.0 m/s the bottom of a loop
b) Using the equation a=v^2/r, calculate the acceleration at the bottom of the loop.
c) Is this a safe acceleration?
Yes
d) At what speed would this loop with radius of 12.0 m begin to be a safety concern?
Yes
e) At what speed would the acceleration in a loop with smaller radius of 7.0 m begin to be a safety concern?
Yes
3. A roller-coaster car is traveling at 25.0 m/s at the bottom of a loop. The radius of the loop is 10.0 m.
a) Calculate the acceleration of the car at the bottom of the loop.
b) Is this a safe acceleration?
This isn't safe because it is greater than 4.
4. A roller coaster has an initial height of 50.0 above the bottom of an incline.
a) What will the speed of the roller-coaster car at the bottom of the incline?
b) The roller-coaster car goes into a loop with a radius of 10.0 m. What is the acceleration required to keep the cart moving in the circular loop?
c) What will be the speed of the roller-coaster car at the top of the loop?
e) Explain whether this roller coaster is safe at the bottom and the top of the loop
The acceleration is safe at the top and the bottom of the loop.
6. A roller-coaster car, when filled with people, has a mass of 900.0kg. The roller-coaster car rounds a curve on the ground with a radius of 18.0 m at a speed of 12.0 m/s
a) What is the centripetal acceleration of the car?
b) What is the centripetal force on the car?
c) What will provide the centripetal force?
Track on wheels
7. A roller-coaster car, when filled with people has a mass of 900.0 kg. The roller-coaster cart rounds a curve on the group with a radius of 15.0 m at a speed of 20.0 m/s.
a) What is the centripetal acceleration of the car?
b) What is the centripetal force on the car?
c) The wheels in the tracks can provide a force of 25,000 N. Is the roller coaster safe? Yes because the Fc is 24,000 and the wheel have 25,000 N
8. A roller coaster is able to complete a loop when the car has two passengers. The car is loaded with six people
a) Will the centripetal acceleration change as a result of the change in mass?
No because mass is not a factor
b) Will the roller coaster be going faster, slower, or the same speed at the bottom of the loop with the extra passengers?
The same speed
c) Will the roller-coaster track require a stronger material because of the increased number of riders?
Yes because the normal force from the track will need to be greater because weight is increasing.
Physics Plus